Finding a rotary switch for a stepped attenuator
 

wrote in message
ups.com...
Hi

Does anyone know where I can source a good quality rotary switch (2
pole and 20 ways) to make a stepped attenuator??

I've looked at previous posts reccommending Blore Edwards but I can't
seem to find them on the web....maybe they're not trading anymore??
Farnell and RS gave me no joy.

I've got a home made amp and I'm currently using a conductive plastic
pot but I'd like to hear the difference in going to a stepped
attenuator.

**You'll certainly hear a difference, alright. 20 steps is utterly
inadequate to resolve the differences in level required for a decent system.
Try 100+ steps and you'll be getting somewhere. To do that, I'd suggest a
relay/resistor matrix is the way to go. The most recent example I've worked
on was in a Conrad Johnson preamp. It was pretty impressive. At least as
good as an Alps 'Blue Velvet' pot. Without the latter's (slightly) superior
ability for fine volume adjustments.

20 steps, you have to be joking!


--
Trevor Wilson
www.rageaudio.com.au



--
Posted via a free Usenet account from http://www.teranews.com

Finding a rotary switch for a stepped attenuator
 

In article , Trevor Wilson
wrote:

wrote in message
ups.com...
Hi

Does anyone know where I can source a good quality rotary switch (2
pole and 20 ways) to make a stepped attenuator??


**You'll certainly hear a difference, alright. 20 steps is utterly
inadequate to resolve the differences in level required for a decent
system. Try 100+ steps and you'll be getting somewhere.

20 steps, you have to be joking!

Oddly enough, I find that 21 steps suits me fine in use. Been using 21-step
attenuators for years, and find both the range of adjustment and the sizes
of the steps are no problem in practice.

Looks like there is a dramatic and unexpected distinction between 20 steps
and 21. :-)

Above said, I'll add two caveats.

1) The above is for domestic replay equipment. If I wanted to adjust levels
in the context of professional 'live' recordings then I'd agree that 20
steps would be insufficient. It would lack the required range and
resolution. But the point here is I find that the recording/broadcast
engineers have already set decent levels to the point where a 21 step seems
to me to cope fine.

2) I do tend to modify the input sensitivity and/or output levels of
sources to avoid the situation where I'm having to switch between a 2V
nominal source and a 150mV nominal one and having to wind the volume
setting up or down around 20dB just to correct for this. This is largely
because I tend to use a mix of 'old fashioned' and 'more modern' sources,
though.

Slainte,

Jim

--
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Finding a rotary switch for a stepped attenuator
 

In article ,
Jim Lesurf wrote:
2) I do tend to modify the input sensitivity and/or output levels of
sources to avoid the situation where I'm having to switch between a 2V
nominal source and a 150mV nominal one and having to wind the volume
setting up or down around 20dB just to correct for this. This is largely
because I tend to use a mix of 'old fashioned' and 'more modern' sources,
though.

Heh heh - I've got amps on the outputs of the DVD recorder, Freeview tuner
- both fed into the TV - and an amp on the output of the new TV to bring
that up to pukka DIN standard phonos of the old Philips this has replaced.
Otherwise it would have meant altering everything else feeding the main
amp, which like you I spent some time getting as near right as possible...

--
*Why is it that rain drops but snow falls?

Dave Plowman London SW
To e-mail, change noise into sound.

Finding a rotary switch for a stepped attenuator
 

In article , Dave Plowman (News)
wrote:
In article , Jim Lesurf
wrote:
2) I do tend to modify the input sensitivity and/or output levels of
sources to avoid the situation where I'm having to switch between a 2V
nominal source and a 150mV nominal one and having to wind the volume
setting up or down around 20dB just to correct for this. This is
largely because I tend to use a mix of 'old fashioned' and 'more
modern' sources, though.

Heh heh - I've got amps on the outputs of the DVD recorder, Freeview
tuner - both fed into the TV - and an amp on the output of the new TV to
bring that up to pukka DIN standard phonos of the old Philips this has
replaced.

In our 'living room' system I use a switch to select between the SPDIF
outputs from the DTTV tuner, the DVD recorder/player, and the CD player.
Fed to a DAC, and then to a Quad 34. This works fine - although I have
altered the sensitivity of the 34 input connected to the DAC. It nominally
means they all are presented to the preamp as coming from a source with the
same output ref/0dB level.

Most of the time the volume setting I use with this system is in the range
from step '5' to '10'. In practice, '5' for TV/DVD/popular music and '10'
for Classical music on CD, etc.

Exceptions being '4' for some exceptionally loud DVDs which seem to be
level compressed to 0dBFS all the time, and around 12-13' for some CDs
recorded from R3 DAB with no level adjustment made during recording.[1]

I also use an FM4 into another input, again with the preamp sensitivity
altered so that I find the range from '5' to '10' is fine for listening to
BBC stations.

The control on the Quad 34 (as is usual for such attenuators) doesn't have
uniform steps. However from my experience a 20- or 21-step with steps of
about 2dB would actually be fine in normal use. The only snag being that
you might want a preamp sensitivity that you can set appropriately for
different inputs (i.e. different signal sources).

FWIW one of the reasons I like the Quad 34 is that the circuit diagrams and
the board layout (with component numbers printed on the PCBs) makes
modifying the input sensitivities, etc, dead easy.

I suspect that if I were designing a preamp for general sale these days,
I'd include a simple way for the user to set the input sensitivites of
individual inputs over a 20dB range, and then provide a 20- or 21-step
attenuator as the volume control. IIUC some amps do this in various ways,
and it seems a sensible approach to me as it overcomes having to use the
volume control to deal with having different sources with inherently
different reference/0dB levels.

Slainte,

Jim

[1] i.e. recorded by feeding SPDIF from a DAB tuner to a CDRecorder with
the digital gain left at 0dB - i.e. the recorder accepting the levels as
presented. The results for R3 concerts seem to show that the level almost
never peaks above about -6dB. i.e. two or three steps on the Quad
attenuator in the range I use.

The 'loudest' DVDs I've come across aren't a blockbuster film. They are the
'Saint' colour TV collection. These seem to have been compressed to death.
Perhaps they assume anyone old enough to want these because they recall
liking the orginal broadcasts must be deaf... ;-

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html